This invention relates generally to fuel injection pumps, and more particularly to electronically controlled, solenoid operated fuel injection pumps of the so-called jerk pump type adapted for use with Diesel and internal combustion engines.
In applying an injection pump to an engine, the pump must fulfil requirements for capacity, injection duration, injection pressure, injection timing and in some cases control rack travel.
Jerk pumps commonly comprise a plunger disposed in an injection barrel which receives an amount of fuel to be pressurized. The plunger is mechanically driven by the engine as by a driving connection with an engine cam shaft so as to produce an injection of fuel at an appropriate point in the engine cycle by movement of the plunger in the barrel towards an injection chamber. The increased pressure in the injection chamber causes the opening of an injection delivery valve to thereby cause injection of the metered fuel charge into the associated engine cylinder.
In the jerk pump, both the quantity of fuel injected into the injection chamber for each injection cycle and also the timing of such fuel injection must be controlled. In the past it has been the practice to provide the plunger with a helical groove which cooperates with ports formed in the barrel to control the bypass of fuel from the injection chamber. In a traditional port-helix jerk pump, injection is terminated when the helix on the plunger covers a spill port in the barrel. When this occurs, depending upon the relative angular position of the helix to the spill port, the quantity of fuel to be delivered has been controlled. (See U.S. Pat. No. 2,922,581 issuing Jan. 26, 1960 to Garday for a Fuel Injection Apparatus). Means have also been provided for rotating the plunger to change the position of the helix within the barrel to produce a variation in bypass flow and hence in the quantity and timing of fuel injection for a giving injection cycle.
This arrangement is relatively simple, reliable and has found widespread application. However, the limits within which the quantity and timing parameters of fuel injection may be varied by such grooves and ports are such that it is difficult to achieve precise control over these parameters for maximum engine efficiency and/or emission control.
In an effort to provide improved control over these parameters, arrangements for providing electrical control over the injection consisting of valving means and associated intensifiers which are operated wholly by electronic fuel control systems have been suggested. U.S. Pat. No. 4,219,154 issuing Aug. 82, 1980 to Luscomb shows an electronically controlled fuel injection system which does not include an accumulator charged by a piston for supplying metered fuel.
In a jerk pump arrangement shown in U.S. Pat. No. 3,779,225 issuing Dec. 18, 1973 to Watson, et al, leakage may be present in the control valving which affects the preciseness and efficiency of the injection process.
Ine one application an electronically controlled valve was provided to provide both injection and metering functions. This pump arrangement required very fast turnaround times of the solenoid in the valve when dealing with small fuel quantities. Also this pump did not deliver a metered fuel charge. It would be desirable to provide an injection system that delivers a metered fuel charge and which has a separate accumulator that supplies pressure without resorting to a separate pump. A built-in accumulator could supply fuel at sufficient pressure to make a servo-valve and spool valve functional and also move a piston during metering.